CERT^® Advisory CA-1993-07 Cisco Router Packet Handling Vulnerability

A complete revision history is at the end of this file.

The CERT Coordination Center has received information indicating that under some circumstances Cisco routers will pass IP source routed packets which should have been denied. Routers which do not use the "no ip source-route" command are not affected. This vulnerability applies to all models of Cisco routers. This problem occurs with the following releases of software: 8.2, 8.3, 9.0, 9.1 and 9.17.

Cisco Systems and CERT recommend that sites using Cisco routers to provide firewall protection take action to eliminate this vulnerability from their networks.

This security issue is fixed in Cisco software releases 8.3(7.2), 9.0(5), 9.1(4) 9.17(2.1) and in all later releases. Customers who are using software release 8.2 must upgrade to a later release and should contact Cisco's Technical Assistance Center (TAC) at 800-553-2447 (Internet: tac@cisco.com ) for more information.

Cisco recommends that customers whose routers may be affected by this vulnerability upgrade their software to the following versions:

    Release  (Update)
      8.3      (8)
      9.0      (5)
      9.1      (4)
      9.17     (3)

These releases are available on Cisco's Customer Information On-Line (CIO) service for those customers having a maintenance contract. Other customers may obtain these releases through Cisco's Technical Assistance Center or by contacting their local Cisco distributor.

I. Description

A vulnerability exists in Cisco routers such that a router which is configured to suppress source routed packets with the following command:

     no ip source-route

may allow traffic which should be suppressed.

II. Impact

This vulnerability can allow unauthorized traffic to pass through the router/gateway.

III. Solution

Cisco recommends that affected customers upgrade to a later version. Customers who cannot upgrade immediately may be able use access lists to prevent unauthorized traffic.

Customers who have questions should contact the Cisco Technical Assistance Center at 800-553-2447 for assistance. Internet: tac@cisco.com

CERT/CC Contact Information

Email: cert@cert.org
Phone: +1 412-268-7090 (24-hour hotline)
Fax: +1 412-268-6989
Postal address:

CERT Coordination Center
Software Engineering Institute
Carnegie Mellon University
Pittsburgh PA 15213-3890
U.S.A.

CERT/CC personnel answer the hotline 08:00-17:00 EST(GMT-5) / EDT(GMT-4) Monday through Friday; they are on call for emergencies during other hours, on U.S. holidays, and on weekends.

Using encryption

We strongly urge you to encrypt sensitive information sent by email. Our public PGP key is available from

http://www.cert.org/CERT_PGP.key

If you prefer to use DES, please call the CERT hotline for more information.

Getting security information

CERT publications and other security information are available from our web site

http://www.cert.org/

* "CERT" and "CERT Coordination Center" are registered in the U.S. Patent and Trademark Office.

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Copyright 1993 Carnegie Mellon University.

September 19,1997  Attached Copyright Statement